1. Field of the Invention
The present invention relates to a plasma monitoring method applicable to a semiconductor manufacturing processes (steps) and all the other manufacturing processes using plasma and a plasma monitoring system therefor.
2. Description of the Related Art
There is a conventional technique related to a plasma monitoring method and a plasma monitoring system for monitoring a processing on a wafer disposed in a plasma processing apparatus as disclosed in, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 2003-282546 and 2005-236199.
FIG. 7 is a schematic configuration diagram showing a conventional plasma monitoring system disclosed in the JP-A Nos. 2003-282546 and 2005-236199.
The plasma monitoring system includes a plasma processing apparatus 10. The plasma processing apparatus 10 is an apparatus applying a radio frequency (hereinafter, “RF”) bias to a plasma chamber 11 set in a vacuum to generate plasma 12 within the plasma chamber 11, and performing such processings as etching and film formation on a wafer 20 that is a monitoring target workpiece disposed on a stage 13. A voltmeter 15 for self-alignment bias measurement is connected to the stage 13 via a coil 14 for alternating current (hereinafter, “AC”) voltage component elimination. A sensor 21 or the like for plasma process detection is bonded onto the wafer 20.
If a plasma process is to be monitored, then the plasma 12 is generated in the plasma chamber 11 by application of the RF bias to the plasma chamber 11, and the plasma process (e.g., plasma etching) is performed on the wafer 20. At this time, by monitoring a voltage detected by the sensor 21, a plasma etching end point may be detected and the wafer 20 may be worked with high accuracy.
It is generally known that energy of ions generated from the plasma 12 during the plasma etching influences a shape and a size of a pattern of the wafer 20 and electrically damages the wafer 20. Due to this, it is important to observe energy of ions incident on the wafer 20 from the plasma 12 and an ion energy distribution. However, since the ion incident energy if ions may not be directly measured, a self-alignment bias is monitored and set as an indirect index. Normally, the voltmeter 15 disposed below the stage 13 within the plasma chamber 11 measures an average value of the self-alignment bias. Since the self-alignment bias is an AC voltage, the coil 14 eliminates RF component in the AC voltage so that the voltmeter 15 may measure only a constant direct-current (hereinafter, “DC”) voltage.
FIG. 8 is a schematic diagram explaining the self-alignment bias. As shown in a state 1, when the wafer 20 is exposed to the plasma 12, the plasma 12 is in a state in which electrons e and positive ions h are slightly separated. Both the electrons e and the positive ions h move to be charged onto the wafer 20. However, at this time, the electrons e more faster and a large quantity of electrons e are charged onto the wafer 20 (and onto the stage 13 if the stage 13 is present under the wafer 20) since the electrons e are far lighter than the positive ions h. Due to this, as shown in a state 2, a potential of the wafer 20 turns negative by the charging of the electrons e on the wafer 20.
As shown in a state 3, the positive ions h which are oppositely charged to electrons e, and which move faster than electrons, arrive at the wafer 20. However, the amount of the positive ions h is not so large as to cancel the electrons e previously charged at the wafer 20. Due to this, ultimately both the negative electrons e and the positive ions h from the plasma 12 arrive at the wafer 20 and are charged thereat. However, since a charge amount of the initial negative electrons e (in the state 1) is larger, the potential of the wafer 20 is negative in a stable state. This negative potential is referred to as self-alignment bias.
Nevertheless, the conventional plasma monitoring methods and plasma monitoring systems have a first problem (1) and a second problem (2) as follows.